Systems for controlling speed, torque and/or position of DC motors are known and have been widely used in a variety of applications including automotive control systems. Generally, such DC motors fall into two broad categories; namely brushed DC motors and brushless DC motors. While brushless DC motors typically offer desirable performance features and certain advantages over brushed DC motors in an automotive environment, such features and advantages may often be offset by the complexity of motor control and motor drive circuits required to accurately control motor operation. For example, controlled stoppage, accurate motor shaft positioning, motor reversal and consistent control of motor output torque are all difficult to achieve with brushless DC motors.
Dedicated systems for controlling and driving brushless DC motors are known. In such systems, a motor control circuit is typically operable to detect motor shaft position as well as motor drive current, and a motor drive circuit is, in turn, responsive to motor control signals supplied by the motor control circuitry to drive the DC motor in a desired manner. In known DC motor drive circuits, the motor driving function is often partitioned into a two-stage drive operation; namely a pre-driver circuit and a power drive circuit. The pre-driver circuit typically serves as an interface between a motor control logic circuit and a power drive device such as a discrete power transistor, wherein the pre-driver circuit is operable to convert the logic level motor control signals to one or more signals suitable for driving the power drive device.
While known pre-driver circuits have been widely used in various DC brushless motor control systems, such pre-driver circuits suffer from several drawbacks, particularly when used in automotive applications. For example, known pre-driver circuits in automotive applications are often strictly analog circuits that suffer from slow response time and high power dissipation. Conversely, while known digital pre-driver circuits may provide for fast and accurate motor control, such systems are typically incapable of supplying such control in a high voltage automotive environment, and are consequently not often used. In either case, electromagnetic interference (EMI) requirements are difficult to satisfy in a high voltage environment, and known pre-driver circuits often suffer from deleterious effects resulting from EMI. What is therefore needed is an improved pre-driver circuit for a motor control system that is both power efficient and capable of high speed operation in a high voltage automotive environment. Ideally, such an improved pre-driver circuit should also be compatible with imposed EMI requirements.